CALIBRATION OF YELLOW COLOUR SPECTROSCOPIC METHOD OF PHOSPHORUS DETERMINATION FOR WAVELENGTH, WORKING RANGE AND TIME

Abstract

Yellow colour spectroscopic method to determine phosphorus in solution is a very accurate and reliable tool used world wide in chemistry laboratories. The working range of this method is up to 20 ppm and the absorbance is read at 470 nm wavelength. The yellow chromogen is quite stable for long time.In this study, the method is revised to find the most suitable wavelength at which the yellow chromogen gives the highest absorbance. This study further investigates the working range within which a linear relationship exists between phosphorus concentration and the absorbance. The stability of the chromogen with time was also studied. From the study it is found that, the yellow colourchromogen absorbs only the lower portion of the visible spectrum and 400 nm light is better to use to get highest light absorbance. The absorption values gradually decreases with the increase in wavelength and at 600 nm wavelength absorption value becomes zero. The working range may extend up to 30 ppm instead of 20 ppm. The chromogen was found stable even for 2 months.